1. Field of the Invention
The present invention relates to a power supply apparatus to which a pre-bias voltage is applied across output terminals from outside even when operation of a converter is stopped.
2. Description of the Related Art
A general switching power supply apparatus including a step-down converter circuit is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2013-207993. This switching power supply apparatus described in Japanese Unexamined Patent Application Publication No. 2013-207993 includes a control circuit that controls a high-side MOSFET and a low-side MOSFET so as to perform synchronous rectification, and is configured to increase power conversion efficiency through the control.
Japanese Unexamined Patent Application Publication No. 10-112942 discloses a power supply apparatus in which power supply apparatuses each including a converter and a secondary battery are connected in parallel and perform parallel operations. Each of the power supply apparatuses in Japanese Unexamined Patent Application Publication No. 10-112942 has a function of modifying the output voltage of the converter.
In a power supply system where a plurality of power supply apparatuses are connected in parallel for parallel operation, as described in Japanese Unexamined Patent Application Publication No. 10-112942, in a power supply apparatus in which a secondary battery, that is, a battery or a power supply circuit including a battery, is connected to the output terminal, a state is generated in which a voltage (hereinafter called a “pre-bias voltage”) from outside, for example, from a battery is applied across the output terminals also during a period when the converter operation is stopped.
In the case where a power supply apparatus including a converter that controls switching devices through feedback control is made to operate by comparing a set voltage and an actual output voltage, as disclosed in Japanese Unexamined Patent Application Publication No. 2013-207993, when a difference between the set value and the present value of the output voltage is too large, the converter may not be activated normally in some cases. For example, a phenomenon is generated in which due to the fact that a difference between the set value and the present value of the output voltage is too large, a protection operation is activated, before the converter is activated, due to the operation of another circuit such as a protection circuit, thereby preventing normal activation.
Further, in the case where the output set voltage is lower than the voltage between output terminals due to a pre-bias voltage, or in the case where the output voltage of the power supply apparatus is transiently low at the time of activation or the like, a reverse current flows from the output terminals to the converter when a converter based on the synchronous rectifying method as disclosed in Japanese Unexamined Patent Application Publication No. 2013-207993 is employed.
Further, in the case where the set value (set voltage) of the output voltage of the power supply apparatus is high, an excessive charge current may flow from the power supply apparatus to a battery.